Please correct my maths

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raysputin
raysputin Posts: 142 Member
in Fitness and Exercise
I am trying to calculate the calorie expenditure when lifting but think that I am getting too high a figure - can someone please confirm my results or tell me what the correct figure is?

Assume a weight of 25Kgs.
Multiply by 9.8 to convert to newtons = 245 N.

Assume a lift height of 1 Metre = 245 Joules.
Convert joules to calories J/4.1858 = 58.5 calories.

That appears to be a lot of calories for one lift.

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  • VeryKatie
    VeryKatie Posts: 5,953 Member
    edited November 2014
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    Remember that the calories we use for our diets are actually kilo calories (bet of a pet peeve of mine that North America generally drops the "k" in "kcal"). So divide by 1000 at the end.... I guess... but that would mean... say you do 30 lifts, that's 1.755 kcal haha. That doesn't make sense either!

    But that's actually why I don't think you can calculate energy burn from our bodies the same way. Remember you'd also be lifting a portion of your body weight, you're also expending more energy because of your organ muscles (heart, lungs, etc.) working harder... there's likely so much more to those calculations including elevation above sea level, oxygen efficiency... and who knows what else.

    I also am not sure where the 1 m = 245 joules comes from, but energy calculations are not my strong point. I like things that don't move. Good ol' statics.
  • raysputin
    raysputin Posts: 142 Member
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    In the effort to be brief I left out the method for calculating joules.

    The method I am using is to multiply the weight by gravity in mtrs/sec (9.8) to convert to newtons and then by the distance moved against gravity in metres to calculate the joules.

    The joule to calorie conversion is straight forward from there.

  • Wronkletoad
    Wronkletoad Posts: 368 Member
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    that's calories and not kilocalories as VK said.

    58.5 calories / 1000 = "Calories" or kcal or dietary calories

    (same reason that drinking a cup of ice-cold water doesn't do anything to make you lose weight -- you'd have to go by degree centigrade per liter)
  • raysputin
    raysputin Posts: 142 Member
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    Ahhh - I see the light. Thank you people. I knew I was wrong somewhere.

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